It is known to produce plexifilamentary products by various methods. For example, they can be produced by mechanically working or "fibrillating" highly oriented sheets, bands, films, foils, ribbons or filaments of synthetic polymers. Another method involves shaping filaments or sheets comprising two or more mutually incompatible polymers, orientating the shaped structure and then mechanically working it to cause fibrillation; alternatively, one of the two incompatible polymers may be dissolved away to leave a fibrillated product.
Plexifilamentary strands can also be produced by flash-extruding a solution of a synthetic organic polymer in an activating organic liquid (comprising a solvent) under superatmospheric pressure and at a temperature in excess of the boiling point of the solvent into a region of lower pressure. The flash extrusion procedure requires the use of organic materials which must be separated and recovered. In addition, such materials create fire and toxicity hazards, and also require the use of costly recovery systems.
The process of this invention avoids the use of organic solvents by employing water in their place, and permits the extremely rapid spinning of plexifilamentary yarn strands from a single-orifice extruder.